Embodiments of the invention relate generally to electric motors and, more particularly, to an asynchronous motor including a component for introducing disturbances into the magnetic field of the motor by altering a reluctance of the motor.
The usage of electrical machines in various industries has continued to become more prevalent in numerous industrial, commercial, and transportation industries over time. Due to the prevalence of these motors in industry, it is paramount that the electric motors be operated reliably and efficiently. Motor design parameters and performance parameters are often required by motor management systems to optimize the control and operations of electric motors. Similarly, motor status monitoring enables the electric motors to operate reliably. Many motor status monitoring techniques also look for certain motor design parameters and performance parameters.
One such motor performance parameter that is helpful in optimizing the control and operations of electric motors is rotor or motor speed. However, a typical induction motor design does not have the ability to measure rotor speed without some form of physical detection sensor. In many applications, sensor location, alignment, size, and environmental conditions make the sensor option extremely difficult to integrate into the design while still maintaining a high level of reliability and robustness.
For example, in an x-ray tube environment, implementation of a physical detection sensor is very challenging because of the increased air gap between the sensor (which would be operating in dielectric oil) and the target material (in vacuum). Additionally, positioning of the x-ray tube casing, which is typically formed of a non-ferrous material such as stainless steel, in the air gap between the stator and the rotor attenuates the magnetic field more than air or vacuum. Also, the sensor target material temperature gradient is critical if the target is a permanent magnet (e.g., magnets formed of Samarium Cobalt, for example, are only rated to 350° C. max). Finally, the size restriction of the sensor itself is a challenge, as it is situated between an x-ray tube's casing and insert housing.
While some systems and techniques for sensorless measurement of rotor speed have been provided in the past, such techniques are typically limited in their implementation. For example, a rotor may be designed to be asymmetrical or have saliencies therein that result in a change in impedance as seen at the stator windings, thereby providing for estimation of the rotor speed based on motor current spectrum analysis based on this change in impedance. However, such signals have a poor signal-to-noise ratio (SNR), which limits the ability to effectively measure such signals. Furthermore, as set forth above, the generation of such signals relies on defects designed into the motor, which is highly undesirable with respect to motor performance (e.g., efficiency, torque capability, etc.).
It would therefore be desirable to design an asynchronous motor that provides for detection of rotor speed that is not dependent on measurements acquired via a physical detection sensor, so as to enable the improved motor management and motor status monitoring of asynchronous motors. It would further be desirable for such an asynchronous motor to provide signals having a high SNR and for such signals to be generated without varying an impedance of the motor via the introduction of defects thereto.